I wouldn´t put plaster in a microwave. Maybe place the bowls in very hot water? I think when I made hump molds I lined the bowls with heavy plastic.
---- allgaul <email@example.com> wrote:
> Hey everybody-
> We are going to attempt the Empty Bowls project at my school so I decided
> the easiest way to make all those bowls would be over plaster hump molds. I
> had ordered pottery plaster to make the molds and got to it yesterday.
> I greased up some heavy plastic bowls from the dollar store with Vaseline
> and poured pottery plaster into them. I tried to get them to release and
> they won't budge! They aren't too big, maybe 8" across and 5" tall. No
> undercuts. Just simple heavy plastic soup bowls-some were rounded inside and
> some had straighter sides and a flat bottom inside. The layer of Vaseline
> was not too thick, but I definitely got the insides and top completely
> covered. I tried to release them about 45 minutes after I poured the
> plaster-it was still warm to the touch. The school day was over and I had to
> leave for an appointment so didn't try again.
> I haven't done this before with plaster and I am wondering if when plaster
> cools down it contracts a bit? If I microwave the bowl, would it heat up the
> plastic and allow me to get the mold out more easily?
> I did 20 molds and really need them after the Thanksgiving break! I should
> have put cheesecloth or plastic wrap to make it easier for myself, but of
> course in hindsight...
> anyway, I know I can cut into the plastic, it would be hard but it would get
> them out. I was hoping to use the bowls again for more molds.
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